1. Field
This disclosure relates to enhancing the properties of coatings that are applied onto glass panels, such as low-E (i.e. low emissivity) glass.
2. Related Art
For many architectural purposes it is desirable to have as low an emissivity and Rs value as feasible, such that the glass window is reflecting substantial amounts of the infrared energy impinging on the glass. Generally speaking, “low-E” (i.e. low emissivity) glasses are considered to be those glasses which have a hemispherical emissivity (Eh) of less than about 0.16 and a normal emissivity (En) of less than about 0.12. Preferably, Eh is about 0.13 or less, and En is about 0.10 or less. At the same time, sheet resistance (Rs) is, therefore, preferably less than about 10.5 ohms/square. Such glasses, to be commercially acceptable, usually are required to transmit as much visible light as possible, often about 76% or more using the Illuminant C technique for measuring transmittance in glasses of about 2 mm-6 mm thick. Visible transmittance, in this respect, should more preferably be at least about 78% or greater for glasses between about 2 mm-6 mm thick. Even more preferably, visible transmittance should be about 80% or greater, and still most preferably, greater than about 80%.
The technique of creating architectural glass by magnetron sputter-coating multiple layers of metal and/or metal oxides or nitrides onto float glass sheets is well known and a large number of permutations and combinations of known metals (e.g. Ag, Au, etc.), oxides and nitrides have been attempted and reported. Such techniques may employ either planar or tubular targets, or a combination of both, in multi-target zones to achieve their desired results. Exemplary of preferred apparatus for use in this invention, and known in the art, is a magnetron sputter-coater sold by Airco Corporation. This commercially available device is disclosed in U.S. Pat. Nos. 4,356,073 and 4,422,916, respectively. The disclosures of these patents are incorporated herein by reference.
In particular, it has been known to use the aforesaid Airco sputter-coater to produce architectural glasses having a layering system, sequentially from the glass (e.g. standard float glass) outwardly, as follows: an undercoat layer of Si3 N4, a first layer of nickel or nickel alloy, a layer of silver, a second layer of nickel or nickel alloy, and an overcoat layer of Si3 N4. As one example, the coating may comprise Si3 N4/Ni:Cr/Ag/Ni:Cr/Si3 N4, in which it has been found in practice that the Ni:Cr alloy is 80/20 by weight Ni/Cr, respectively (i.e. nichrome), and wherein the two nichrome layers are reported as being 7 Å thick, the Ag layer is specified as being only about 70 Å thick, and the Si3 N4 layers are relatively thicker (e.g. 320 Å for the undercoat and about 450 Å for the overcoat). In reality, because of its thinness (i.e. about 70 Å), the silver (Ag) layer has been found, in practice, to actually be rather semi-continuous in nature. In certain instances, these layer system consists essentially of a seven-layer system created by severing the silver layer into two silver layers with a nickel-based (e.g. nickel-chrome) layer in between, such that the layer system from the glass outwardly now consists essentially of: Si3 N4/Ni:Cr/Ag/Ni:Cr/Ag/Ni:Cr/Si3 N4.
The problem is the films are not typically durable and can be damaged easily in handling and shipping. The industry typically puts a removable protective thin film over the final layer to protect the low e coatings from damage due to handling and the environment. In other instances a permanent hard coating is provided, such as diamond-like coating (DLC) to enhance the scratch resistance of the low-E coating. Two examples are illustrated in FIGS. 1A and 1B, using DLC and Zirconium dioxide (zirconia), respectively.